Aluminum alloys



Patented Oct. 31, 1933 PATENT OFFICE ALUMINUM ALLOYS Walter A. Dean and Louis W. Kempf, Cleveland,

Ohio, assignors to Aluminum Company of America, Pittsburgh, Pennsylvania Pa., a corporation of No Drawing. Application September 21, 1932 Serial No. 634,157

Claims.

This invention relates to aluminum base alloys and has as its principal object the provision of alloys which may be readily cast into permanent molds to produce comparatively light strong 5 castings capable of retaining a substantial proportion of their strength and elongation at elevated temperatures. A further object of the invention is the provision of a casting alloy which may be used in either sand or permanent mold,

foundry to produce such castings as require a high surface finish and a good resistance to corrosion.

The aluminum base alloys containing magnesium are extremely light and are likewise strong. Such alloys, however, do not, in binary form, meet all of the requirements of a good foundry alloy. Moreover, light alloy castings are in demand for use as reciprocating parts which operate at elevated temperatures and the binary m aluminum-magnesium alloys do not have, in

many instances, the temperatures.

We have discovered that the properties of certain of the binary aluminum-magnesium alloys may be substantially improved by the addition thereto of certain limited amounts of nickel. The presence of nickel in the alloy is more efiicient, we have discovered, in maintaining the original ductility of the alloy at high temperature than any other alloying element to us known. The nickel improves the strength of the alloy at elevated temperatures without reducing the ductility to as large an extent as do the other hardening elements. In experimenting with such alloys we have discovered that those alloys containing 3.0 to 7.5 per cent by weight of magnesium and 0.2 to 2.0 per cent by weight of nickel, the balance being principally aluminum, are peculiarly adapted to use at high temperatures and offer, for that purpose, a combination of lightness, strength and ductility seldom encountered in structural material. We have, moreover, found that these alloys have excellent foundry characteristics and can be used in the production of intricate castings. Whileparticularly adapted to the manufacture of permanent mold castings, the alloys are likewise amenable to casting in sand molds and can, therefore, be used in an all-purpose foundry with considerable success.

When the alloys are cast into permanent molds, We prefer to use a somewhat narrower composition range, the preferred alloys for this purpose containing 3.5 to 4.5 per cent by weight of magnesium and 0.25 to 1.0 per cent by weight properties desired at high of nickel, the balance being principally aluminum. A preferred alloy is one containing 4 per cent by weight of magnesium and 0.75 per cent by weight of nickel. Such alloys handle very well in the foundry and are particularly adapted co to the manufacture of cooking utensils or other castings of fairly thin section which, in the finished condition, should be resistant to mild forms of corrosion and should present a lasting polished surface.

The high temperature properties of our novel alloys are excellent. For instance, an alloy containing 6.0 per cent by weight of magnesium, the balance being principally aluminum, in sand cast form after heating for 4 hours at 700 Fahrenheit and then 20 days at 600 Fahrenheit had, at that temperature, a tensile strength of 15,000 pounds per square inch and an elongation of 5 per cent in 2 inches. A similar alloy, similarly treated but containing 1.5 per cent of nickel, had a tensile strength of 17,000 pounds per square inch and an elongation of 7.2 per cent in 2 inches. Thus it will be seen that the addition of nickel to the alloy has raised the tensile strength at high temperature and has not decreased the elongation but has, in fact, increased it. For this purpose amounts of nickel in the order of 1.0 to 2.0 per cent are particularly desirable.

Another property of these alloys is their improved fluidity as compared with the alloys which have, heretofore, been Widely used as a material for parts operating at elevated temperatures. Comparative tests, based upon the distance that the molten alloy, originally heated to a given temperature, will flow through a spiral formed in a sand mold, have shown that our novel alloys are very superior with respect to fluidity.

In further experimenting with these alloys, we have discovered that the addition thereto of a very small amount of a class of elements herein defined to be antimony and bismuth will increase both strength and ductility at elevated temperatures. The amount of antimony or bismuth which may be added is limited, the amount being 0.05 to 0.4 per cent by weight of the total alloy. If added in amounts greater than about 0.4 per cent, the elfect is reversed and the elongation of the alloy is reduced. Either antimony or bismuth or both metals may be used but'in total they should not exceed about 0.4 per cent.

The alloys of our invention may be compounded in the usual fashion by melting the aluminum and adding thereto the other metals either singly or in alloy form. Likewise any other commercial method of alloying will be found to be satisfactory.

The aluminum used in the manufacture of the alloys may be of the highest purity or it may contain amounts of usual impurities, and the term aluminum as used .herein and in the claims designates the aluminum of commerce. It is an incidental property of our alloys that the presence of iron in amounts as high as 2 per cent by weight is not harmful tothe high temperature properties of the alloys and, therefore, a wide choice between the various grades of commercial aluminum is possible.

We claim:

1. A metallic alloy characterized by high physical and tensile properties at elevated tempera- 4.5 per cent by weight of magnesium and 0.25 to 1.0 per cent by weight of nickel, the balance being aluminum.

3. A metallic alloy characterized by high physical and tensile properties at elevated temperatures and good fluidity and consisting of 4.0 per cent by weight of magnesium and 0.75 per cent by weight of nickel, the balance being aluminum.

4. A metallic alloy characterized by high physical and tensile properties at elevated temperatures and good fluidity and consisting of 6.0 per cent by weight of magnesium and 1.5 per cent by weight of nickel, the balance being aluminum.

5. A metallic alloy characterized by high physical and tensile properties at elevated temperatures and good fluidity and consisting of 6.0 per cent by weight of magnesium and 1.0 to 2.0 per cent by weight of nickel, the balance being aluminum.

WALTER A. DEAN. LOUIS W. KEMPF. 

